The present disclosure generally relates to an adjustable classifier that can adjust the size of particles separated in a solid fuel mill.
Power plants employ solid fuel furnaces in boilers for various purposes, such as for generating steam to create electric power.
The solid fuel, typically coal, is pulverized into a powder that is blown into the furnace to be burned. Mills (or pulverizers) are used to pulverize coal into powder. The mills typically create a distribution of particles sizes. However, for combustion, particles above a given size do not completely burn and therefore, fuel is wasted.
However, if all particles are pulverized to a very fine size, energy required to pulverize the particles is wasted. Also, the throughput of mill particles drops significantly when all particles are required to be very small. This would then require additional mills, which can become very expensive.
Therefore, there is a tradeoff of particle size in which balances the amount of coal that will be unburned vs. the throughput requires to efficiently run the boiler.
The particle size chosen is determined on how long it takes to burn the particle and how much unburned fuel is acceptable.
The particles are blown through the furnace and based upon their speed have a limited time in the furnace to burn. The rate of burning is related to the mass of the fuel to be burned, the surface area of the particles, the energy of the furnace flames, the water content and the type of fuel used. If all of these factors are fixed and the classifier is designed to separate particles with a size corresponding to these factors, the system runs well. However, if one or more of these factors changes necessitating different sized particles to be used, conventional classifiers are not easily modified to separate different sized particles.
Currently, there is a need for an adjustable classifier that can adjust the particles size distribution that is allowed to exit the mill and is fed to the boiler.
A classifier system 100 for separating coarser particles from finer particles entrained in an upward air stream is described having:
a housing 110 having a general circular cross section;
a truncated cone 120 inside of the housing 110 having a larger section at its top and a small cone outlet 230 at its bottom, the cone 120 defining an inner chamber 125;
an outer chamber 190 between the housing and the cone 120 adapted to receive coarser and finer particles entrained in the upward air stream;
a classifier ring 130 at the top of the cone 120 having a frame 133 with a plurality of windows 131 with vanes 140 hinged adjacent to each window 131; wherein the vanes 140 are adjustable to partially or fully close the windows 131 thereby affecting the size of particles allowed through them and into the inner chamber 125;
a fuel tube outlet 240 above the classifier ring 130 adapted to allow the air stream to exit the classifier system 100.
The invention may also include:
an adjustment system 260 having:
at least one pressure sensor 263 upstream of the classifier ring 130 to measure air pressure entering the classifier ring 130;
at least one pressure sensor 261 downstream of the classifier ring 130 to measure air pressure exiting the classifier ring 130;
a coarseness sensing device 269 adapted to sense particle size exiting the fuel tube outlet 240; and
a control unit 265 adapted to receive signals from the sensors and calculate a vane 140 setting.
The disclosure may be understood more readily by reference to the following detailed description of the various features of the disclosure and the examples included therein.